The present invention relates to a biological test pack of the type used in hospital sterilization procedures. In particular, the invention relates to a biological test pack of the type used in ethylene oxide (EO) sterilization procedures.
Ethylene oxide gas is commonly used in sterilizing items for use in health care facilities. A common method of testing for the efficacy of the EO sterilization process is to include a biological indicator in the load being sterilized. A biological indicator is a suspension of a large number of bacterial spores that has been dried on a carrier, e.g., paper, and then inserted into a package, such as a glassine envelope or a plastic vial. The spore suspension is typically comprised of a bacterial species that is very resistant to EO. For example, Bacillus subtilis may be used, and it may be present on the carrier in large numbers. Accordingly, the spore suspension acts as an indicator for the effectiveness of the EO sterilization process. If large numbers of a very EO resistant organism are placed in a load, and if the sterilization process kills those resistant spores, then it is reasonable to conclude that the EO sterilization process was effective.
Since most items that are being EO sterilized are held in some sort of packaging which is intended to maintain the sterility of the contents of the pack until the time of their use, it is prudent to enclose the biological indicator inside similar packaging in order to equalize the challenge of killing the spores on the biological indicator.
In order to standardize the packaging challenge, the Association for the Advancement of Medical Instrumentation (AAMI) has issued an AAMI Recommended Practice entitled "Good Hospital Practice: Performance Evaluation of Ethylene Oxide Sterilizers--Ethylene Oxide Test Packs". That document recommends the use of a standardized routine test pack for general purpose EO sterilizers in which the biological indicator as well as a chemical indicator can be positioned, and also a more resistant challenge pack for newly installed EO sterilizers. The recommended standard challenge test packs consist of a plastic syringe enclosing a biological indicator, the syringe being wrapped in a properly-sized cotton towel, and this entire assembly enclosed inside a wrapping or pouch.
The making of an EO test pack is often a tedious process, as the test packs are laborious to construct, and not all of the necessary materials and components may be present at the institution. In addition, there is no standardized method of manufacturing or selecting the components. Compounding this problem is the fact that the surgical towel component of the test pack, which acts as a heat sink and moisture absorber in the test pack, is inherently susceptible to variation, because surgical towels are subject to large changes in their characteristics. For example, after each successive laundering, a surgical towel loses some of its fiber content and thus its capacity to provide a heat and moisture challenge. If it is laundered and then ironed, the towel may be so dry that it provides too much of a challenge to moisture absorption.
In order to minimize the above problems, it would be desirable to have an EO indicator test pack that yields the same rate of survival or death of a biological indicator as does the AAMI-described pack, but which would be fully disposable (no need to stockpile pack materials for reuse). It would also be desirable to have such a test pack be of standardized construction to eliminate variations from pack to pack, and to have it be preloaded with an appropriate biological indicator to eliminate labor required for assembly. Such a pack should behave in a manner which is equivalent to the biological indicator test pack recommended by AAMI for routine use in general purpose EO sterilizers. A challenge test pack is somewhat different from a test pack used for routine general purpose monitoring in that it provides more of a challenge to spore kill. A challenge test pack is used primarily during installation and validation of a new or repaired EO sterilizer. It is also desirable that the test pack yield results consistent with the results of the challenge test pack described by AAMI.